Did you know there are two windows of time during the day when it’s impossible or nearly impossible to fall asleep?
Let’s walk through the sleep day:
If you wake up naturally, without an alarm, when your body is genuinely ready, you enter your first wake maintenance zone; you couldn’t fall asleep if you tried. Your sleep debt’s paid off (ideally) and your hormones are at a circadian peak, keeping your body alert and ready.
In the afternoon, your sleep debt has accumulated some and you experience a circadian dip, which generates a secondary sleep propensity (*in about 60% of people). Many people are familiar with this mid-day dip in energy. This is an ideal time for a nap!
And then in the evening you’ll have another period of alertness when you couldn’t fall asleep if you wanted to — the second wake maintenance zone or the “forbidden zone” for sleep. This second circadian peak could come anywhere between 4pm and midnight, depending on your biorhythms. (College age humans are “phase delayed,” so their forbidden zone is likely to come later, rather than sooner.) Whenever it is, this is an excellent time to do homework, have a deep conversation with a friend, or be creative.
Two hours after this, the “sleep gate” opens and you become increasingly inclined to sleep. Within 4 hours, sleep becomes hard to resist. This is your primary sleep propensity phase.
Then you wake up in the morning and start all over!